如何按顺序在ExecutorService中执行任务？

我有三个连接的线程，即第二个线程在第一个死后执行。

这是我的代码：

public class Main { public static void main(String args[]) throws Exception { final Thread thrdA = new Thread(() -> System.out.println("Message 1")); final Thread thrdB = new Thread(() -> System.out.println("Message 2")); final Thread thrdC = new Thread(() -> System.out.println("Message 3")); thrdA.start(); thrdA.join(); thrdB.start(); thrdB.join(); thrdC.start(); thrdC.join(); } } 

如何使用ExecutorService而不是三个线程对象实现此function？

Answer 1

如果您想要/需要的是一个接一个地执行一组作业但是在与主应用程序线程不同的单个线程中，则使用Executors#newSingleThreadExecutor 。

 ExecutorService es = Executors.newSingleThreadExecutor(); es.submit(() -> System.out.println("Message 1")); es.submit(() -> System.out.println("Message 2")); es.submit(() -> System.out.println("Message 3")); es.shutdown(); 

Answer 2

您可以使用带有future.get（）方法的SingleThread ExecutorService来控制线程的顺序执行。

DummyTask类

 import java.util.concurrent.Callable; public class DummyTask implements Callable { int taskId; public DummyTask(int taskId) { this.taskId = taskId; } @Override public Integer call() throws Exception { System.out.println("excuting task... Task Id: " + taskId); return taskId; } } 

SequentialExecution类

 package com.amit.executorservice; import java.util.concurrent.ExecutionException; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.Future; public class SequentialExecution { public static void main(String[] args) throws InterruptedException, ExecutionException { DummyTask task1 = new DummyTask(1); DummyTask task2 = new DummyTask(2); DummyTask task3 = new DummyTask(3); Future result = null; ExecutorService executor = Executors.newSingleThreadExecutor(); result = executor.submit( task1 ); // future.get() Waits for the task to complete, and then retrieves its result. result.get(); result = executor.submit( task2 ); // future.get() Waits for the task to complete, and then retrieves its result. result.get(); result = executor.submit( task3 ); // future.get() Waits for the task to complete, and then retrieves its result. result.get(); executor.shutdown(); } } 

产量

 excuting task... Task Id: 1 excuting task... Task Id: 2 excuting task... Task Id: 3 

输出将始终相同，所有任务将按顺序执行。

Answer 3

如果您已在应用程序中使用线程池，则可以通过零线程代理串行执行程序重用它，而无需创建特殊的单线程线程池。 Executor接口的javadoc部分描述了一个实现，另一个是优化的实现，在我的Github存储库CodeSamples中 。